Chemical and photochemical behavior of ruthenium nitrosyl complexes with terpyridine ligands in aqueous media

Ruthenium nitrosyl complexes with NO release capability: the use of fluorene as an antenna

A ruthenium nitrosyl complex of formula [RuII(fluorene(C6)CH2O-terpy)(bipy)(NO)]3+ (AC) in which fluorene(C6) is the 9,9-dihexylfluorene, terpy the 2,2';6',2''-terpyridine, and bipy the 2,2'-bipyridine is presented with its related [RuII(MeO-terpy)(bipy)(NO)]3+ (C) and 9,9-dihexylfluorene 2-hydroxymethylfluorene (A) building blocks. The reference complex C undergoes NO release capabilities under irradiation at λ = 365 nm. The effect of the introduction of the fluorescent A antenna within the resulting AC complex is discussed both experimentally and theoretically. The importance of the encaging parameter defined as ϕAC·IAC, in which IAC is the quantity of light absorbed by AC and ϕAC the quantum yield of NO release is evidenced and found to be concentration dependent. The conditions of optimization of the antenna approach to maximize ϕAC·IAC are discussed. The crystal structure of [RuII(fluorene(C6)CH2O-terpy)(bipy)(NO2)](PF6), the last intermediate in the synthesis of AC is also presented.

Photorelease of Nitric Oxide (NO) in Mono- and Bimetallic Ruthenium Nitrosyl Complexes: A Photokinetic Investigation with a Two-Step Model

Two monometallic and three bimetallic ruthenium acetonitrile (RuMeCN) complexes are presented and fully characterized. All of them are built from the same skeleton [FTRu(bpy)(MeCN)]2+, in which FT is a fluorenyl-substituted terpyridine ligand and bpy is the 2,2'-bipyridine. The crystal structure of [FTRu(bpy)(MeCN)](PF6)2 is presented. A careful spectroscopic analysis allows establishing that these 5 RuMeCN complexes can be identified as the product of the photoreaction of 5 related RuNO complexes, investigated as efficient nitric oxide (NO) donors. Based on this set of complexes, the mechanism of the NO photorelease of the bimetallic complexes has been established through a complete investigation under irradiations performed at 365, 400, 455, and 490 nm wavelength. A two-step (A → B → C) kinetic model specially designed for this purpose provides a good description of the mechanism, with quantum yields of photorelease in the range 0.001-0.029, depending on the irradiation wavelength. In the first step of release, the quantum yields (ϕAB) are always found to be larger than those of the second step (ϕBC), at any irradiation wavelengths.

Insight into the anti-proliferation activity and photoinduced NO release of four nitrosylruthenium isomeric complexes and their HSA complex adducts

Four Ru(II)-centered isomeric complexes [RuCl(5cqn)(Val)(NO)] (1-4) were synthesized with 5cqn (5-chloro-8-hydroxyquinoline) and chiral Val (Val = L- or D-valine) as co-ligand, and their structures were confirmed using the X-ray diffraction method. The cytotoxicity and photodynamic activity of the isomeric complexes and their human serum albumin (HSA) complex adducts were evaluated. Both the isomeric complexes and their HSA complex adducts significantly affected HeLa cell proliferation, with an IC50 value in the range of 0.3-0.5 μM. The photo-controlled release of nitric oxide (NO) in solution was confirmed using time-resolved Fourier transform infrared and electron paramagnetic resonance spectroscopy techniques. Furthermore, photoinduced NO release in living cells was observed using a selective fluorescent probe for NO. Moreover, the binding constants (Kb) of the complexes with HSA were calculated to be 0.17-1.98 × 104 M-1 and the average number of binding sites (n) was found to be close to 1, it can serve as a crucial carrier for delivering metal complexes. The crystal structure of the HSA complex adduct revealed that one [RuCl(H2O)(NO)(Val)]+ molecule binds to a pocket in domain I. This study provides insight into possible mechanism of metabolism and potential applications for nitrosylruthenium complexes.

Effect of Electron-donating Group on NO Photolysis of {RuNO}6 Ruthenium Nitrosyl Complexes with N2 O2 Lgands Bearing π-Extended Rings

In this study, we introduced the electron-donating group (-OH) to the aromatic rings of Ru(salophen)(NO)Cl (0) (salophenH2 =N,N'-(1,2-phenylene)bis(salicylideneimine)) to investigate the influence of the substitution on NO photolysis and NO-releasing dynamics. Three derivative complexes, Ru((o-OH)2 -salophen)(NO)Cl (1), Ru((m-OH)2 -salophen)(NO)Cl (2), and Ru((p-OH)2 -salophen)(NO)Cl (3) were developed and their NO photolysis was monitored by using UV/Vis, EPR, NMR, and IR spectroscopies under white room light. Spectroscopic results indicated that the complexes were diamagnetic Ru(II)-NO+ species which were converted to low-spin Ru(III) species (d5 , S=1/2) and released NO radicals by photons. The conversion was also confirmed by determining the single-crystal structure of the photoproduct of 1. The photochemical quantum yields (ΦNO s) of the photolysis were determined to be 0>1, 2, 3 at both the visible and UV excitations. Femtosecond (fs) time-resolved mid-IR spectroscopy was employed for studying NO-releasing dynamics. The geminate rebinding (GR) rates of the photoreleased NO to the photolyzed complexes were estimated to be 0≃1, 2, 3. DFT and TDDFT computations found that the introduction of the hydroxyl groups elevated the ligand π-bonding orbitals (π (salophen)), resulting in decrease of the HOMO-LUMO gaps in 1-3. The theoretical calculations suggested that the Ru-NNO bond dissociations of the complexes were mostly initiated by the ligand-to-ligand charge transfer (LLCT) of π(salophen)→π*(Ru-NO) with both the visible and UV excitations and the decreasing ΦNO s could be explained by the changes of the electronic structures in which the photoactivable bands of 1-3 have relatively less contribution of transitions related with Ru-NO bond than those of 0.

A Trojan horse approach for enhancing the cellular uptake of a ruthenium nitrosyl complex

Ruthenium nitrosyl (RuNO) complexes continue to attract significant research interest due to several appealing features that make these photoactivatable nitric oxide (NO˙) donors attractive for applications in photoactivated chemotherapy. Interesting examples of molecular candidates capable of delivering cytotoxic concentrations of NO˙ in aqueous media have been discussed. Nevertheless, the question of whether most of these highly polar and relatively large molecules are efficiently incorporated by cells remains largely unanswered. In this paper, we present the synthesis and the chemical, photophysical and photochemical characterization of RuNO complexes functionalized with 17α-ethinylestradiol (EE), a semisynthetic steroidal hormone intended to act as a molecular Trojan horse for the targeted delivery of RuNO complexes. The discussion is centered around two main molecular targets, one containing EE (EE-Phtpy-RuNO) and a reference compound lacking this biological recognition fragment (Phtpy-RuNO). While both complexes displayed similar optical absorption profiles and NO˙ release efficiencies in aqueous media, important differences were found regarding their cellular uptake towards dermal fibroblasts, with EE-Phtpy-RuNO gratifyingly displaying a remarkable 10-fold increase in cellular uptake when compared to Phtpy-RuNO, thus demonstrating the potential drug-targeting capabilities of this biomimetic steroidal conjugate.

Acetylacetonate Ruthenium Nitrosyls: A Gateway to Nitric Oxide Release in Water under Near-Infrared Excitation by Two-Photon Absorption

A fundamental challenge for phototriggered therapies is to obtain robust molecular frameworks that can withstand biological media. Photoactivatable nitric oxide (NO) releasing molecules (photoNORMs) based on ruthenium nitrosyl (RuNO) complexes are among the most studied systems due to several appealing features that make them attractive for therapeutic applications. Nevertheless, the propensity of the NO ligand to be attacked by nucleophiles frequently manifests as significant instability in water for this class of photoNORMs. Our approach to overcome this limitation involved enhancing the Ru-NO π-backbonding to lower the electrophilicity at the NO by replacing the commonly employed 2,2'-bipyridine (bpy) ligand by an anionic, electron-rich, acetylacetonate (acac). A versatile and convenient synthetic route is developed and applied for the preparation of a large library of RuNO photoNORMs with the general formula [RuNO(tpy)(acac)]2+ (tpy = 2,2':6',2″-terpyridine). A combined theoretical and experimental analysis of the Ru-NO bonding in these complexes is presented, supported by extensive single-crystal X-ray diffraction experiments and by topological analyses of the electron charge density by DFT. The enhanced π-back-bonding, systematically evidenced by several techniques, resulted in a remarkable stability in water for these complexes, where significant NO release efficiencies were recorded. We finally demonstrate the possibility of obtaining sophisticated water-stable multipolar NO-delivery platforms that can be activated in the near-IR region by two-photon absorption (TPA), as demonstrated for an octupolar complex with a TPA cross section of 1530 GM at λ = 800 nm and for which NO photorelease was demonstrated under TPA irradiation in aqueous media.

Insight into novel anti-mucormycosis therapies: investigation of new anti-mucormycosis laser-induced photodynamic therapy based on a sulphone bis-compound loaded silica nanoemulsion

For drug delivery applications, silica nanoemulsion encapsulated with organic compounds are becoming increasingly more desirable. Therefore, the emphasis of this research was on the synthesis of a new potent antifungal drug-like candidate (1,1'-((sulfonylbis(4,1-phenylene)bis(5-methyl-1H-1,2,3-triazole-1,4-diyl))bis(3-(dimethylamino)prop-2-en-1-one), SBDMP), the chemical structure of which was confirmed on the basis of its spectral and microanalytical data. Then, silica nanoemulsion loaded with SBDMP was prepared using Pluronic F-68 as a potent surfactant. The particle shape, hydrodynamic size, and zeta potential of the produced silica nanoemulsion (with and without drug loading) were assessed. The antitumoral activity of the synthesized molecules showed the superiority of SBDMP and silica nanoemulsion with and without SBDMP loading against Rhizopus microsporous and Syncephalastrum racemosum. Subsequently, the laser-induced photodynamic inactivation (LIPDI) of Mucorales strains was determined using the tested samples. The optical properties of the samples were investigated using UV-vis optical absorption and the photoluminescence. The photosensitivity of the selected samples appeared to enhance the eradication of the tested pathogenic strains when exposed to a red (640 nm) laser light. The optical property results verified that the SBDMP-loaded silica nanoemulsion has a high depth of penetration into biological tissues due to a two-absorption photon (TAP) mechanism. Interestingly, the photosensitizing of the nanoemulsion loaded with a newly synthesized drug-like candidate, SBDMP, opens up a new route to apply new organic compounds as photosensitizers under laser-induced photodynamic therapy (LIPDT).

A ruthenium nitrosyl complex-based highly selective colorimetric sensor for biological H2S and H2S-NO cross-talk regulated release of NO

A ruthenium nitrosyl complex (1·NO) and 1·NO incorporated phospholipid-based liposomes (Lip-1·NO) were reported for highly selective colorimetric detection of H₂S. The probe 1·NO "cross-talks" with H₂S and releases nitric oxide (NO) in the process. The detection limit for H₂S was found to be 0.31 μM and 0.45 μM in the cases of 1·NO and Lip-1·NO, respectively. The DAF-FM DA assay has been performed to confirm the H₂S-induced NO release from 1·NO and Lip-1·NO. The sensing of H₂S was also verified by ESI-MS and FT-IR spectroscopy. It was also observed that external stimuli, H₂S and light worked in an almost similar way to release NO as observed by UV-Vis spectroscopy. A molecular logic gate operation "OR" was applied to the probe 1·NO in combination with inputs 'light' and 'H₂S' to give the output 'NO release'. Hence, the probe 1·NO performs the dual work of sensing H₂S with a colorimetric response, releasing NO upon cross-talk between NO and H₂S.

Photodissociation of nitric oxide from designed ruthenium nitrosyl complex: Studies on wound healing and antibacterial activity

A photoactivable NO releasing complex [Ru(L^1-2)(PPh₃)(NO)Cl₂](PF₆)(1a) have been synthesized by complex [RuL^1-2(PPh₃)₂Cl₂](1). Newly designed bidentate ligands, i.e., 4-methoxy-N'-phenyl-N'-(pyridin-2-ylmethyl)benzohydrazide(L¹) and 4-nitro-N'-phenyl-N'-(pyridin-2-ylmethyl)benzohydrazide (L²) were utilized to synthesize complex (1). Complex (1) was characterized by ESI-MS, and the solid structure of the complex [1a](PF₆) was acquired by X-ray crystallography. Different spectroscopic techniques were employed for the identification of ligands (L¹ and L²) and complexes (1 and [1a](PF₆)). Calculations employing DFT and TD-DFT were made better to understand the electronic properties of the complex [1a](PF₆). The photo liberation experiments were screened in the presence of visible light lamp. Griess assay experiment was used to quantify the photo released amount to NO. The photo liberated NO was successfully transferred to reduced myoglobin (Mb). The complex [1a](PF₆) at 50 μg/mL concentration was used for wound healing and antimicrobial activity on B16F1 mouse skin cells and Escherichia coli bacteria, respectively. In results, we observed a considerable wound healing activity of [1a](PF₆) complex after 36 h of incubation in the light-treated cells compared to the control medium, and also it shows more than 99% inhibition of bacterial cells after 1.5 h of treatment in the presence of light. These study suggested that this complex 1a](PF₆) could be utilized for topical delivery of NO for combating several dermatological infections.

Visible-light NO photolysis of ruthenium nitrosyl complexes with N2O2 ligands bearing π-extended rings and their photorelease dynamics

NO photorelease and its dynamics for two {RuNO}⁶ complexes, Ru(salophen)(NO)Cl (1) and Ru(naphophen)(NO)Cl (2), with salen-type ligands bearing π-extended systems (salophenH₂ = N,N'-(1,2-phenylene)-bis(salicylideneimine) and naphophenH₂ = N,N'-1,2-phenylene-bis(2-hydroxy-1-naphthylmethyleneimine)) were investigated. NO photolysis was performed under white room light and monitored by UV/Vis, EPR, and NMR spectroscopies. NO photolysis was also performed under 459 and 489 nm irradiation for 1 and 2, respectively. The photochemical quantum yields of the NO photolysis (Φ_NO) of both 1 and 2 were determined to be 9% at the irradiation wavelengths. The structural and spectroscopic characteristics of the complexes before and after the photolysis confirmed the conversion of diamagnetic Ru(II)(L)(Cl)-NO⁺ to paramagnetic S = ½ Ru(III)(L)(Cl)-solvent by photons (L = salophen^2- and naphophen^2-). The photoreleased NO radicals were detected by spin-trapping EPR. DFT and TDDFT calculations found that the photoactive bands are configured as mostly the ligand-to-ligand charge transfer (LLCT) of π(L) → π*(Ru-NO), suggesting that the NO photorelease was initiated by the LLCT. Dynamics of NO photorelease from the complexes in DMSO under 320 nm excitation were investigated by femtosecond (fs) time-resolved mid-IR spectroscopy. The primary photorelease of NO occurred for less than 0.32 ps after the excitation. The rate constants (k_-1) of the geminate rebinding of NO to the photolyzed 1 and 2 were determined to be (15 ps)^-1 and (13 ps)^-1, respectively. The photochemical quantum yields of NO photolysis (Φ_NO, λ = 320 nm) were estimated to be no higher than 14% for 1 and 11% for 2, based on the analysis of the fs time-resolved IR data. The results of fs time-resolved IR spectroscopy and theoretical calculations provided some insight into the overall kinetic reaction pathway, localized electron pathway or resonance pathway, of the NO photolysis of 1 and 2. Overall, our study found that the investigated {RuNO}⁶ complexes, 1 and 2, with planar N₂O₂ ligands bearing π-extended rings effectively released NO under visible light.

Ruthenium-nitrosyl complexes as NO-releasing molecules and potential anticancer drugs

The synthesis of new types of mono- and polynuclear ruthenium nitrosyl complexes is driving progress in the field of NO generation for a variety of applications. Light-induced Ru-NO bond dissociation...

The Ruthenium Nitrosyl Moiety in Clusters: Trinuclear Linear μ-Hydroxido Magnesium(II)-Diruthenium(II), μ3-Oxido Trinuclear Diiron(III)-Ruthenium(II), and Tetranuclear μ4-Oxido Trigallium(III)-Ruthenium(II) Complexes

The ruthenium nitrosyl moiety, {RuNO}⁶, is important as a potential releasing agent of nitric oxide and is of inherent interest in coordination chemistry. Typically, {RuNO}⁶ is found in mononuclear complexes. Herein we describe the synthesis and characterization of several multimetal cluster complexes that contain this unit. Specifically, the heterotrinuclear μ₃-oxido clusters [Fe₂RuCl₄(μ₃-O)(μ-OMe)(μ-pz)₂(NO)(Hpz)₂] (6) and [Fe₂RuCl₃(μ₃-O)(μ-OMe)(μ-pz)₃(MeOH)(NO)(Hpz)][Fe₂RuCl₃(μ₃-O)(μ-OMe)(μ-pz)₃(DMF)(NO)(Hpz)] (7·MeOH·2H₂O) and the heterotetranuclear μ₄-oxido complex [Ga₃RuCl₃(μ₄-O)(μ-OMe)₃(μ-pz)₄(NO)] (8) were prepared from trans-[Ru(OH)(NO)(Hpz)₄]Cl₂ (5), which itself was prepared via acidic hydrolysis of the linear heterotrinuclear complex {[Ru(μ-OH)(μ-pz)₂(pz)(NO)(Hpz)]₂Mg} (4). Complex 4 was synthesized from the mononuclear Ru complexes (H₂pz)[trans-RuCl₄(Hpz)₂] (1), trans-[RuCl₂(Hpz)₄]Cl (2), and trans-[RuCl₂(Hpz)₄] (3). The new compounds 4–8 were all characterized by elemental analysis, ESI mass spectrometry, IR, UV–vis, and ¹H NMR spectroscopy, and single-crystal X-ray diffraction, with complexes 6 and 7 being characterized also by temperature-dependent magnetic susceptibility measurements and Mössbauer spectroscopy. Magnetometry indicated a strong antiferromagnetic interaction between paramagnetic centers in 6 and 7. The ability of 4 and 6–8 to form linkage isomers and release NO upon irradiation in the solid state was investigated by IR spectroscopy. A theoretical investigation of the electronic structure of 6 by DFT and ab initio CASSCF/NEVPT2 calculations indicated a redox-noninnocent behavior of the NO ancillary ligand in 6, which was also manifested in TD-DFT calculations of its electronic absorption spectrum. The electronic structure of 6 was also studied by an X-ray charge density analysis.

Mononuclear trans-[Ru(OH)NO(Hpz)₄]²⁺ proved to be a source of μ-hydroxido and μ₃- and/or μ₄-oxido bridging groups, which could be incorporated into the heterotrinuclear complexes {[Ru(μ-OH)(μ-pz)₂(pz)(NO)(Hpz)]₂Mg}, [Fe₂RuCl₄(μ₃-O)(μ-OMe)(μ-pz)₂(NO)(Hpz)₂], and [Fe₂RuCl₃(μ₃-O)(μ-OMe)(μ-pz)₃(MeOH)(NO)(Hpz)][Fe₂RuCl₃(μ₃-O)(μ-OMe)(μ-pz)₃(DMF)(NO)(Hpz)] (7·MeOH·2H₂O) and the heterotetranuclear μ₄-oxido complex [Ga₃RuCl₃(μ₄-O)(μ-OMe)₃(μ-pz)₄(NO)]. The structures obtained were all confirmed by SC-XRD, including an X-ray charge density analysis that revealed the electronic structure of the RuFe2 cluster. Two of these nitrosyl complexes underwent photoinduced isomerization with generation of the nitrosyl linkage isomers MS1 and MS2, as revealed by IR spectroscopy at 10 K.

Nitric oxide release and related light-induced cytotoxicity of ruthenium nitrosyls with coordinated nicotinate derivatives

The synthetic approaches for the preparation of trans(NO,OH)-cis(NO₂,NO₂)-[RuNO(L)₂(NO₂)₂OH], where L = ethyl nicotinate (I) and methyl nicotinate (II), are reported. The structures of the complexes are characterized by X-ray diffraction and analyzed by Hirshfeld surface analysis. Both compounds show a nitric oxide release reaction under 445 or 532 nm irradiation of dimethyl sulfoxide (DMSO) solutions, which is studied by combined ultraviolet-visible- (UV-vis), infrared- (IR), and electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT) calculations. The charge transfer from the OH-Ru-NO chain and nitrite ligands to the antibonding orbitals of Ru-NO is responsible for the photo-cleavage of the ruthenium-nitrosyl bond. The elimination of NO leads to a side reaction, namely the protonation of the parent hydroxyl compound. The cytotoxicity and photo-induced cytotoxicity investigations of both compounds on the breast adenocarcinoma cell line MCF-7 reveal that (I) and (II) are cytotoxic with IC₅₀ values of 27.5 ± 2.8 μM and 23.3 ± 0.3 μM, respectively. Moreover, (I) shows an increase of the toxicity after light irradiation by 7 times (IC₅₀ = 4.1 ± 0.1), which makes it a prominent target for deeper biological investigations.

Synthesis, Biomacromolecular Interactions, Photodynamic NO Releasing and Cellular Imaging of Two [RuCl(qn)(Lbpy)(NO)]X Complexes

Two light-activated NO donors [RuCl(qn)(Lbpy)(NO)]X with 8-hydroxyquinoline (qn) and 2,2′-bipyridine derivatives (Lbpy) as co-ligands were synthesized (Lbpy₁ = 4,4′-dicarboxyl-2,2′-dipyridine, X = Cl⁻ and Lbpy₂ = 4,4′-dimethoxycarbonyl-2,2′-dipyridine, X = NO₃⁻), and characterized using ultraviolet–visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (¹H NMR), elemental analysis and electrospray ionization mass spectrometry (ESI-MS) spectra. The [RuCl(qn)(Lbpy₂)(NO)]NO₃ complex was crystallized and exhibited distorted octahedral geometry, in which the Ru–N(O) bond length was 1.752(6) Å and the Ru–N–O angle was 177.6(6)°. Time-resolved FT-IR and electron paramagnetic resonance (EPR) spectra were used to confirm the photoactivated NO release of the complexes. The binding constant (K_b) of two complexes with human serum albumin (HSA) and DNA were quantitatively evaluated using fluorescence spectroscopy, Ru-Lbpy₁ (K_b~10⁶ with HSA and ~10⁴ with DNA) had higher affinity than Ru-Lbpy₂. The interactions between the complexes and HSA were investigated using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) and EPR spectra. HSA can be used as a carrier to facilitate the release of NO from the complexes upon photoirradiation. The confocal imaging of photo-induced NO release in living cells was successfully observed with a fluorescent NO probe. Moreover, the photocleavage of pBR322 DNA for the complexes and the effect of different Lbpy substituted groups in the complexes on their reactivity were analyzed.

The π-donor/acceptor trans effect on NO release in ruthenium nitrosyl complexes: a computational insight

The NO release using ruthenium tetraamine complexes was finally elucidated from DFT calculations, highlighting the influence of the acidic medium.

Nitrosyl linkage photoisomerization in heteroleptic fluoride ruthenium complexes derived from labile nitrate precursors

Four complexes with trans-ON–Ru–F coordinate were synthesized from their nitrate precursors. Upon light irradiation, complexes I–III show reversible formation of highly stable linkage isomers MS2 which leads to a higher photogeneration temperature of MS1.

A photoredox catalysed Heck reaction via hole transfer from a Ru(ii)-bis(terpyridine) complex to graphene oxide

The attachment of homoleptic Ru bis-terpy complexes on graphene oxide significantly improved the photocatalytic activity of the complexes. These straightforward complexes were applied as photocatalysts in a Heck reaction. Due to covalent functionalization on graphene oxide, which functions as an electron reservoir, excellent yields were obtained. DFT investigations of the charge redistribution revealed efficient hole transfer from the excited Ru unit towards the graphene oxide.

Two-Photon-Triggered NO Release via a Ruthenium-Nitrosyl Complex with a Star-Shaped Architecture

We report herein a molecular engineering strategy based on the design of a multipolar ruthenium-nitrosyl (Ru-NO) complex with a three-branched architecture. The three Ru-NO units are introduced at the periphery of a highly π-delocalized truxene core bearing three terpyridine ligands. The two-photon absorption capabilities of the complex were investigated by the Z-scan technique. The strong electronic coupling among the individual arms gives rise to a very strong two-photon absorption response (δ_800 nm ∼ 1600 GM), which corresponds to a 16-fold enhancement of the capability of a single-arm reference, thereby promoting an efficient light-driven NO release process in aqueous media.

Near-IR light-induced photorelease of nitric oxide (NO) on ruthenium nitrosyl complexes: formation, reactivity, and biological effects

Polypyridyl backbone nitrosyl complexes of ruthenium with the molecular framework [RuII(antpy)(bpy)NO+/˙]n+ [4](PF6)3 (n = 3), [4](PF6)2 (n = 2), where antpy = 4'-(anthracene-9-yl)-2,2':6',2''-terpyridine and bpy = 2,2'-bipyridine, were synthesized via a stepwise synthetic route from the chloro precursor [RuII(antpy)(bpy)(Cl)](PF6) [1](PF6) and [RuII(antpy)(bpy)(CH3CN)](PF6)2 [2](PF6)2 and [RuII(antpy)(bpy)(NO2)](PF6) [3](PF6). After column chromatographic purification, all the synthesized complexes were fully characterized using different spectroscopic and analytical techniques including mass spectroscopy, 1H NMR, FT-IR and UV-vis spectrophotometry. The Ru-NO stretching frequency of [4](PF6)3 was observed at 1941 cm-1, which suggests moderately strong Ru-NO bonding. A massive shift in the νNO frequency occurred at Δν = 329 cm-1 (solid) upon reducing [4](PF6)3 to [4](PF6)2. To understand the molecular integrity of the complexes, the structure of [3](PF6) was successfully determined by X-ray crystallography. The redox properties of [4](PF6)3 were thoroughly investigated together with the other precursor complexes. The rate constants for the first-order photo-release of NO from [4](PF6)3 and [4](PF6)2 were determined to be 8.01 × 10-3 min-1 (t1/2 ∼ 86 min) and 3.27 × 10-2 min-1 (t1/2 ∼ 21 min), respectively, when exposed to a 200 W Xenon light. Additionally, the photo-cleavage of Ru-NO occurred within ∼2 h when [4](PF6)3 was irradiated with an IR light source (>700 nm) at room temperature. The first-order rate constant of 9.4 × 10-3 min-1 (t1/2 ∼ 73 min) shows the efficacy of the system and its capability to release NO in the photo-therapeutic window. The released NO triggered by light was trapped by reduced myoglobin, a biologically relevant target protein. The one-electron reduction of [4](PF6)3 to [4](PF6)2 was systematically carried out chemically (hydrazine hydrate), electrochemically and biologically. In the biological reduction, it was found that the reduction is much slower with double-stranded DNA compared to a single-stranded oligonucleotide (CAAGGCCAACCGCGAGAAGATGAC). Moreover, [4](PF6)3 exhibited significant photo-toxicity to the VCaP prostate cancer cell line upon irradiation with a visible light source (IC50 ∼ 8.97 μM).

Ruthenium nitrosyl complexes with the molecular framework [RuII(dmdptz)(bpy)(NO)]n+ (dmdptz: N,N-dimethyl-4,6-di(pyridin-2-yl)-1,3,5-triazin-2-amine and bpy: 2,2′-bipyridine). Electronic structure, reactivity aspects, photorelease, and scavenging of NO

Two ruthenium nitrosyl complexes have been stabilized both in {Ru–NO}⁶ and {Ru–NO}⁷ configurations which show facile photocleavage of Ru–NO bond on exposure to visible light. The photo liberated NO is captured by reduced myoglobin.